Exon 2, which encodes the first 69 amino acids (including the initiator methionine), and surrounding intronic sequence were replaced with a neomycin selection cassette. RT-PCR and sequence analysis showed the presence of an aberrantly spliced transcript in which exon 1 had joined exon 3. The aberrant transcript was shown by Western blot analysis to produce a 37kDa protein via an in-frame translational start site at nucleotide 571 (aa 93). The mutant protein lacks the Ets DNA-binding domain.